kmail prefix folder

Hi,
I've just upgraded kde to 3.5 and I have problems with kmail.
Before that, I was using the prefix "Mail" but now this option doesn't exist
anymore. My folders looks like that now :
+Account
|-INBOX
|+Mail
|-Folder1
|-Folder2
|-Folder3
How can I modify kmail options to make it look like before?
I've read some posts about this, but, in fact, I don't have understand
anything. Can someone help me?
Thank you.
Xavier